Implement "Call to the Arms"-button.
This allows a player to task entities to drop off their resources and subsequently attack-move to a specified location with one button.
Patch by: @JCWasmx86
Icon by: @Stan
Differential revision: https://code.wildfiregames.com/D4149
Fixes: #1364
Comments by: @Langbart
Based on a patch by: @Freagarach (https://code.wildfiregames.com/D1868)